U.S. patent number 8,795,848 [Application Number 12/991,129] was granted by the patent office on 2014-08-05 for indolocarbazole derivative with fused heterocyclic aromatic group for organic electroluminescent device and organic electroluminescent device containing same.
This patent grant is currently assigned to Nippon Steel & Sumikin Chemical Co., Ltd.. The grantee listed for this patent is Takahiro Kai, Masaki Komori, Toshihiro Yamamoto. Invention is credited to Takahiro Kai, Masaki Komori, Toshihiro Yamamoto.
United States Patent |
8,795,848 |
Kai , et al. |
August 5, 2014 |
Indolocarbazole derivative with fused heterocyclic aromatic group
for organic electroluminescent device and organic
electroluminescent device containing same
Abstract
Disclosed is an organic electroluminescent device (organic EL
device) that is improved in the luminous efficiency, fully secured
of the driving stability, and of a simple structure and also
disclosed is a compound for organic EL device useful for the said
device. The compound for organic EL device is, for example, an
indolocarbazole derivative represented by the following general
formula (3). The organic EL device comprises a light-emitting layer
disposed between an anode and a cathode piled one upon another on a
substrate and the said light-emitting layer comprises a
phosphorescent dopant and the aforementioned indolocarbazole
derivative as a host material. In general formula (3), L is an
aromatic heterocyclic group of a fused-ring structure with a
valence of (n+1), Ar.sub.1 to Ar.sub.3 each is an alkyl group, an
aralkyl group, or a substituted or unsubstituted aromatic
hydrocarbon or aromatic heterocyclic group, and n is an integer of
0-5. ##STR00001##
Inventors: |
Kai; Takahiro (Kitakyushu,
JP), Komori; Masaki (Kitakyushu, JP),
Yamamoto; Toshihiro (Kitakyushu, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kai; Takahiro
Komori; Masaki
Yamamoto; Toshihiro |
Kitakyushu
Kitakyushu
Kitakyushu |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
Nippon Steel & Sumikin Chemical
Co., Ltd. (Tokyo, JP)
|
Family
ID: |
41264651 |
Appl.
No.: |
12/991,129 |
Filed: |
April 30, 2009 |
PCT
Filed: |
April 30, 2009 |
PCT No.: |
PCT/JP2009/058524 |
371(c)(1),(2),(4) Date: |
November 05, 2010 |
PCT
Pub. No.: |
WO2009/136595 |
PCT
Pub. Date: |
November 12, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110062429 A1 |
Mar 17, 2011 |
|
Foreign Application Priority Data
|
|
|
|
|
May 8, 2008 [JP] |
|
|
2008-122059 |
|
Current U.S.
Class: |
428/690; 546/160;
313/504; 546/167; 548/418; 546/88; 428/917; 257/40 |
Current CPC
Class: |
C09K
11/06 (20130101); C07D 487/04 (20130101); C09B
57/10 (20130101); C09B 47/00 (20130101); H05B
33/20 (20130101); C09B 67/0033 (20130101); C09B
57/00 (20130101); H01L 51/0072 (20130101); C09K
2211/1011 (20130101); C09K 2211/1007 (20130101); C09K
2211/1029 (20130101); C09K 2211/1044 (20130101); C09K
2211/185 (20130101); H01L 51/5016 (20130101); Y10S
428/917 (20130101) |
Current International
Class: |
H01L
51/54 (20060101); C09K 11/06 (20060101); C07D
471/04 (20060101); C07D 471/14 (20060101); C07D
487/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1 956 022 |
|
Aug 2008 |
|
EP |
|
11-167215 |
|
Jun 1999 |
|
JP |
|
2001-313178 |
|
Nov 2001 |
|
JP |
|
2004-204234 |
|
Jul 2004 |
|
JP |
|
2006-193729 |
|
Jul 2006 |
|
JP |
|
WO 01/41512 |
|
Jun 2001 |
|
WO |
|
WO 2006/122630 |
|
Nov 2006 |
|
WO |
|
WO 2007/063754 |
|
Jun 2007 |
|
WO |
|
WO 2008/146839 |
|
Dec 2008 |
|
WO |
|
Other References
English Translation of International Preliminary Report on
Patentability and Written Opinion of the International Searching
Authority, dated Dec. 23, 2010, for International Application No.
PCT/JP2009/058524 (Forms PCT/IB/338, PCT/IB/373 and PCT/ISA/237).
cited by applicant .
International Search Report, dated Jun. 9, 2009, issued in
PCT/JP2009/058524. cited by applicant .
International Preliminary Report of Patentability for
PCT/JP2009/058524 dated Nov. 9, 2010 (Forms PCT/IB/326, PCT/IB/373
and PCT/ISA/237). cited by applicant.
|
Primary Examiner: Bohaty; Andrew K
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Claims
The invention claimed is:
1. A compound for an organic electroluminescent device represented
by the following general formula (1): ##STR00023## wherein ring a
is an aromatic or heterocyclic ring fused to two adjacent rings and
represented by formula (a1), and ring b is a heterocyclic ring
fused to two adjacent rings and represented by formula (b1); X is
CR or N; L is an aromatic heterocyclic group of a fused-ring
structure with a valence of (n+1); Ar.sub.1 and Ar.sub.3 each is
independently an alkyl group, an aralkyl group, or a
C.sub.6-C.sub.15 substituted or unsubstituted aromatic hydrocarbon
or C.sub.3-C.sub.15 substituted or unsubstituted aromatic
heterocyclic group and Ar.sub.3 is never a nitrogen-containing
six-membered ring; R and R.sub.1 to R.sub.5 each is independently
hydrogen, an alkyl group, an aralkyl group, an alkenyl group, an
alkynyl group, a cyano group, a nitro group, an alkoxyl group, an
alkylsulfonyl group, a haloalkyl group, a hydroxyl group, or a
substituted or unsubstituted aromatic hydrocarbon group; and n is
an integer of 0-5.
2. The compound for an organic electroluminescent device as
described in claim 1, wherein the compound is represented by the
following general formula (2): ##STR00024## wherein ring b, L,
Ar.sub.1, R.sub.1 to R.sub.4, and n of formula (2) have the same
meanings as ring b, L, Ar.sub.1, R.sub.1 to R.sub.4, and n,
respectively, of general formula (1).
3. The compound for an organic electroluminescent device as
described in claim 1, wherein the compound is represented by the
following general formula (3): ##STR00025## wherein L, Ar.sub.1,
Ar.sub.3, R.sub.1 to R.sub.4, and n of formula (3) have the same
meanings as L, Ar.sub.1, Ar.sub.3, R.sub.1 to R.sub.4, and n,
respectively, of general formula (1).
4. The compound for an organic electroluminescent device as
described in claim 1, wherein, in general formula (1), L is an
aromatic heterocyclic group of a fused-ring structure containing 6
to 20 carbon atoms with a valence of (n+1).
5. An organic electroluminescent device comprising an organic layer
comprising the compound for an organic electroluminescent device
described in any one of claims 1 to 3.
6. The organic electroluminescent device as described in claim 5,
wherein the organic layer comprising a compound for an organic
electroluminescent device is at least one layer selected from the
group consisting of a light-emitting layer, a hole-transporting
layer, a hole-injecting layer, an electron-transporting layer, an
electron-injecting layer, and a hole-blocking layer.
7. The organic electroluminescent device as described in claim 5,
wherein the organic layer comprising a compound for organic
electroluminescent device is a light-emitting layer and the said
light-emitting layer comprises a phosphorescent dopant and the said
compound for organic electroluminescent device as a host
material.
8. The compound for an organic electroluminescent device as
described in claim 1, wherein the compound has only one
indolocarbazole group.
9. The compound for an organic electroluminescent device as
described in claim 1, wherein L is an unsubstituted aromatic
heterocyclic group of a fused-ring structure composed of 2-3 rings
with a valence of (n+1).
10. The compound for an organic electroluminescent device as
described in claim 1, wherein L is the aromatic heterocyclic group
selected from the group consisting of benzothiophene,
benzothiazole, thianthrene, isobenzofuran, benzoxazole, chromene,
xanthene, phenoxathiin, indolizine, isoindole, indole,
benzimidazole, indazole, benzotriazole, purine, quinolizine,
isoquinoline, quinoline, phthalazine, naphthyridine, quinoxaline,
quinazoline, cinnoline, pterizine, carbazole, carboline,
phenanthridine, acridine, perimidine, phenanthroline, phenazine,
phenothiazine, phenoxazine, and dibenzodioxin.
Description
FIELD OF TECHNOLOGY
This invention relates to a novel compound for organic
electroluminescent device and to an organic electroluminescent
device (hereinafter referred to as organic EL device) using the
said novel compound.
BACKGROUND TECHNOLOGY
An organic electroluminescent device in the simplest structure is
generally constituted of a light-emitting layer and a pair of
counter electrodes sandwiching the said light-emitting layer. The
device functions by utilizing the following phenomenon; upon
application of an electrical field between the electrodes,
electrons are injected from the cathode and holes are injected from
the anode and they recombine in the light-emitting layer with
emission of light.
In recent years, organic thin films have been used in the
development of organic EL devices. In particular, in order to
enhance the luminous efficiency, the kind of electrodes has been
optimized for the purpose of improving the efficiency of injecting
carriers from the electrodes and a device has been developed in
which a hole-transporting layer composed of an aromatic diamine and
a light-emitting layer composed of 8-hydroxyquinoline aluminum
complex (hereinafter referred to as Alq3) are disposed in thin film
between the electrodes. This device has brought about a marked
improvement in the luminous efficiency over the conventional
devices utilizing single crystals of anthracene and the like and
thereafter the developmental works of organic EL devices have been
directed toward commercial applications to high-performance flat
panels featuring self-luminescence and high-speed response.
In another effort to enhance the luminous efficiency of the device,
the use of phosphorescence in place of fluorescence is
investigated. The aforementioned device comprising a
hole-transporting layer composed of an aromatic amine and a
light-emitting layer composed of Alq3 and many other devices
utilize fluorescence. The use of phosphorescence, that is, emission
of light from the excited triplet state, is expected to enhance the
luminous efficiency three to four times that of the conventional
devices utilizing fluorescence (emission of light from the excited
singlet state). To achieve this objective, the use of coumarin
derivatives and benzophenone derivatives in the light-emitting
layer was investigated, but these derivatives merely produced
luminance at an extremely low level. Europium complexes were also
investigated in trials to utilize the excited triplet state, but
they failed to emit light at high efficiency. In recent years, as
is mentioned in patent document 1, a large number of researches are
conducted with the objective of enhancing the luminous efficiency
and extending the lifetime while giving priority to utilization of
organic metal complexes such as iridium complexes. Patent document
1: JP2003-515897 A Patent document 2: JP2001-313178 A Patent
document 3: JP2002-352957 A Patent document 4: JP 11-162650 A
Patent document 5: JP 11-176578 A Patent document 6:
WO2007/063796
In order to enhance the luminous efficiency, a host material to be
used together with a dopant material becomes important. Of the host
materials proposed thus far, a typical example is
4,4'-bis(9-carbazolyl)biphenyl (hereinafter referred to as CBP), a
carbazole compound cited in patent document 2. When CBP is used as
a host material for tris(2-phenylpyridine)iridium complex
(hereinafter referred to as Ir(ppy)3), a phosphorescent material
emitting green light, the balance of electrical charges in the
light-emitting layer is destroyed and excess holes flow out to the
side of the cathode on account of the electron transport property
being inferior to the hole transport property in the case of CBP
and the result is lowering of the luminous efficiency due to
lowering of the recombination probability in the light-emitting
layer. Furthermore, in this case, the recombination zone in the
light-emitting layer is limited to a narrow space in the vicinity
of the interface on the cathode side. Consequently, in the case
where an electron-transporting material, such as Alq3, whose lowest
triplet energy level is lower than that of Ir(ppy)3 is used, there
may arise a possibility that the luminous efficiency becomes lower
due to transfer of the triplet energy from the dopant to the
electron-transporting material.
On the other hand, 3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole
(hereinafter referred to as TAZ), disclosed in patent document 3,
is also proposed as a host material for a phosphorescent organic EL
device. As the hole transport property is inferior to the electron
transport property in the case of TAZ, the light-emitting zone is
on the side of the hole-transporting layer. In this case, the
chosen hole-transporting material influences the luminous
efficiency of Ir(ppy)3. For example, the use of
4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (hereinafter
referred to as NPB), a material in widespread use for its good
performance, high reliability, and long life, in the
hole-transporting layer causes a problem that transfer of the
triplet energy occurs from Ir(ppy)3 to NPB reflecting the
relationship of the lowest triplet energy level between the two and
the luminous efficiency becomes lower.
Furthermore, compounds like CBP and TAZ readily undergo
crystallization and agglomeration with the resultant deterioration
of the shape of thin film. In addition, the Tg of such compounds is
difficult to merely observe because of their high crystallinity.
The instability of the shape of thin film in the light-emitting
layer exerts an adverse influence on the device such as shortening
of the lifetime and lowering of the heat resistance.
As the aforementioned examples indicate, it can readily be
understood that a demand is created for host materials that possess
simultaneously a high hole transport property and a high electron
transport property and are well balanced in the electrical charges
(hole and electron) transport properties. Furthermore, it is
desirable that the host materials are endowed with electrochemical
stability, high heat resistance, and good stability in the
amorphous state.
Further, although patent documents 4, 5, and 6 disclose the use of
a certain kind of indolocarbazole compounds in organic EL devices,
there is a strong demand for compounds with better properties for
use in organic EL devices.
DISCLOSURE OF THE INVENTION
In applications of organic EL devices to display devices such as
flat panel displays, it is necessary to enhance the luminous
efficiency of the device and, at the same time, to fully secure the
driving stability of the device. Under the aforementioned
circumstances, an object of this invention is to provide an organic
EL device of high efficiency, good driving stability, and practical
usefulness and to provide a compound suitable therefor.
The inventors of this invention have conducted intensive studies,
found as a result that the use of compounds of a specified
structure in organic EL devices solves the aforementioned problems,
and completed this invention.
Accordingly, this invention relates to an organic EL device using a
compound of a specified indolocarbazole skeleton.
According to this invention, a compound for organic
electroluminescent device is represented by the following general
formula (1).
##STR00002##
In general formula (1), ring a is an aromatic or heterocyclic ring
fused to two adjacent rings and represented by formula (a1) or
(a2), ring a' is an aromatic or heterocyclic ring fused to three
adjacent rings and represented by formula (a1), and ring b is a
heterocyclic ring fused to two adjacent rings and represented by
formula (b1); X is CR or N; L is an aromatic heterocyclic group of
a fused-ring structure with a valence of (n+1); Ar.sub.1 to
Ar.sub.3 each is independently an alkyl group, an aralkyl group, or
a substituted or unsubstituted aromatic hydrocarbon or aromatic
heterocyclic group and Ar.sub.2 and Ar.sub.3 are never
nitrogen-containing six-membered rings; R and R.sub.1 to R.sub.7
each is independently hydrogen, an alkyl group, an aralkyl group,
an alkenyl group, an alkynyl group, a cyano group, a dialkylamino
group, a diarylamino group, a diaralkylamino group, an amino group,
a nitro group, an acyl group, an alkoxycarbonyl group, a carboxyl
group, an alkoxyl group, an alkylsulfonyl group, a haloalkyl group,
a hydroxyl group, an amide group, or a substituted or unsubstituted
aromatic hydrocarbon or aromatic heterocyclic group and in the case
where any two of the foregoing are located adjacent to each other,
they may be linked to form a ring; n is an integer of 0-5.
The compounds for organic electroluminescent devices represented by
general formula (1) include compounds represented by the following
general formula (2) or (3).
##STR00003##
In general formula (2), ring b, L, Ar.sub.1, R.sub.1 to R.sub.4,
and n respectively have the same meaning as ring b, L, Ar.sub.1,
R.sub.1 to R.sub.4, and n in general formula (1).
##STR00004##
In formula (3), L, Ar.sub.1, Ar.sub.3, R.sub.1 to R.sub.4, and n
respectively have the same meaning as L, Ar.sub.1, Ar.sub.3,
R.sub.1 to R.sub.4, and n in general formula (1).
Further, this invention relates to an organic electroluminescent
device that comprises an organic layer comprising the
aforementioned compound for organic electroluminescent device.
Advantageously, the said organic layer is at least one layer
selected from a light-emitting layer, a hole-transporting layer, a
hole-injecting layer, an electron-transporting layer, an
electron-injecting layer, and a hole-blocking layer. More
advantageously, this invention relates to an organic
electroluminescent device in which the organic layer is a
light-emitting layer and the said light-emitting layer comprises a
phosphorescent dopant and the aforementioned compound for organic
electroluminescent device as a host material.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows the cross section of an example of an organic EL
device.
PREFERRED EMBODIMENTS OF THE INVENTION
The compound for organic EL device of this invention is represented
by the aforementioned general formula (1). Any of the compounds
represented by general formula (1) typically has an indolocarbazole
skeleton formed by fusion of a carbazole ring and an indole ring.
The N atom in the carbazole ring is linked to L, an aromatic
heterocyclic group of a fused-ring structure.
In general formula (1), ring a is an aromatic or heterocyclic ring
fused to two adjacent rings and represented by formula (a1) or
(a2). In the case where ring a is a heterocyclic ring represented
by formula (a2), ring a' is an aromatic or heterocyclic ring fused
to three adjacent rings and represented by formula (a1). In formula
(a1), X is CR or N. Here, R is a group similar to R.sub.1 to
R.sub.7 and it is preferably a hydrogen atom. Ring b is a
heterocyclic ring fused to two adjacent rings and represented by
formula (b1).
In general formula (1), L is an aromatic heterocyclic group of a
fused-ring structure with a valence of (n+1). Here, n is an integer
of 0-5, preferably an integer of 0-2.
Preferable examples of aromatic heterocyclic groups of a fused-ring
structure are the groups formed by removing (n+1) hydrogen atoms
from the aromatic heterocyclic compounds shown below.
Concretely, examples of the aforementioned aromatic heterocyclic
compounds include benzothiophene, benzothiazole, thianthrene,
isobenzofuran, benzoxazole, chromene, xanthene, phenoxathiin,
indolizine, isoindole, indole, benzimidazole, indazole,
benzotriazole, purine, quinolizine, isoquinoline, quinoline,
phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline,
pterizine, carbazole, carboline, phenanthridine, acridine,
perimidine, phenanthroline, phenazine, phenothiazine, phenoxazine,
and dibenzodioxin.
In general formulas (1), (2), and (3), Ar.sub.1 to Ar.sub.3 each is
independently an alkyl group, an aralkyl group, or a substituted or
unsubstituted aromatic hydrocarbon or aromatic heterocyclic group.
However, Ar.sub.2 and Ar.sub.3 are never nitrogen-containing
six-membered rings when the two are aromatic heterocyclic
groups.
In general formulas (1), (2), and (3), the number of carbon atoms
in Ar.sub.1 to Ar.sub.3 is preferably 1 to 6 in the case of an
alkyl group, 7 to 13 in the case of an aralkyl group, or 3 to 15 in
the case of a substituted or unsubstituted aromatic hydrocarbon or
aromatic heterocyclic group.
Preferable examples of the unsubstituted aromatic hydrocarbon
groups are the monovalent groups formed by removing one hydrogen
atom from benzene, naphthalene, anthracene, phenanthrene, indene,
biphenyl, terphenyl, and quaterphenyl. More preferable are the
monovalent groups formed by removing one hydrogen atom from
benzene, biphenyl, and terphenyl.
Preferable examples of the unsubstituted aromatic heterocyclic
groups include the monovalent groups formed by removing one
hydrogen atom from thiophene, thiazole, furan, oxazole, pyran,
pyrrole, imidazole, pyrazole, isothiazole, isoxazole, frazan,
triazole, pyridine, pyrazine, pyrimidine, pyridazine, triazine,
benzothiophene, benzothiazole, thianthrene, isobenzofuran,
benzoxazole, chromene, xanthene, phenoxathiin, indolizine,
isoindole, indole, benzimidazole, indazole, benzotriazole, purine,
quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine,
quinoxaline, quinazoline, cinnoline, pterizine, carbazole,
carboline, phenanthridine, acridine, perimidine, phenanthroline,
phenazine, phenothiazine, phenoxazine, and dibenzodioxin. More
preferable are the monovalent groups formed by removing one
hydrogen atom from pyridine, pyrazine, pyrimidine, pyridazine, and
triazine.
The groups R.sub.1 to R.sub.7 each is independently hydrogen, an
alkyl group, an aralkyl group, an alkenyl group, an alkynyl group,
a cyano group, a dialkylamino group, a diarylamino group, a
diaralkylamino group, an amino group, a nitro group, an acyl group,
an alkoxycarbonyl group, a carboxyl group, an alkoxyl group, an
alkylsulfonyl group, a haloalkyl group, a hydroxyl group, an amide
group, or a substituted or unsubstituted aromatic hydrocarbon or
aromatic heterocyclic group. In the case where any two of the
foregoing are located adjacent to each other, they may be linked to
form a fused ring. Preferably, R.sub.1 to R.sub.7 each is hydrogen
or an alkyl group.
In the case where R.sub.1 to R.sub.7 each is an alkyl group, the
number of carbon atoms in such alkyl group is preferably 1 to 6.
Likewise, the number of carbon atoms is preferably 2 to 6 in the
case of an alkenyl or alkynyl group, 7 to 13 in the case of an
aralkyl group, 3 to 15 in the case of a substituted or
unsubstituted aromatic hydrocarbon or aromatic heterocyclic group,
2 to 10 in the case of a dialkylamino group, 6 to 20 in the case of
a diarylamino or diaralkylamino group, 2 to 10 in the case of an
acyl or alkoxycarbonyl group, and 1 to 6 in the case of an alkoxyl,
alkylsulfonyl, or haloalkyl group.
In the case where any two of R.sub.1 to R.sub.7 are located
adjacent to each other, they may be linked together to form a fused
ring. For example, when two vinyl groups are located adjacent to
each other, the carbon atoms in the vinyl groups and two carbon
atoms in the indolocarbazole skeleton carrying the vinyl groups are
linked together to form a six-membered ring and the result is the
formation of a nitrogen-containing compound of six fused rings. In
the case where there are two pairs of adjacent substituents, there
may be a possibility of the formation of a nitrogen-containing
compound of seven fused rings.
In the case where the aforementioned groups Ar.sub.1 to Ar.sub.3
and R.sub.1 to R.sub.7 are substituted aromatic hydrocarbon or
aromatic heterocyclic groups, preferable substituents include an
alkyl group of 1 to 6 carbon atoms, an alkoxyl group of 1 to 6
carbon atoms, an aryloxy group of 6 to 12 carbon atoms, an
alkylthio group, a substituted amino group, an acetyl group, a
phenyl group, a biphenylyl group, a terphenylyl group, a naphthyl
group, a pyridyl group, a pyrimidyl group, a triazyl group, an
imidazolyl group, a thienyl group, and a carbazolyl group.
General formulas (2) and (3) show preferred forms of general
formula (1); ring a in general formula (1) is specified as a
benzene ring in general formula (2) and the mode of linkage of ring
b is specified in general formula (3).
The compounds for organic EL device of this invention can be
prepared easily by one of known methods. For example, a compound
represented by general formula (1) can be prepared by a sequence of
reactions illustrated below with reference to a synthetic example
described in Synlett., 2005, No. 1, pp. 42-48.
##STR00005##
Preferable examples of the compounds represented by general formula
(1) or by general formulas (2) and (3) are shown below, but are not
limited thereto.
##STR00006## ##STR00007## ##STR00008## ##STR00009## ##STR00010##
##STR00011## ##STR00012## ##STR00013## ##STR00014##
##STR00015##
The compound for organic electroluminescent device of this
invention provides an excellent organic electroluminescent device
when it is incorporated in the organic layer of the device.
Advantageously, the compound is incorporated in at least one
organic layer selected from a light-emitting layer, a
hole-transporting layer, an electron-transporting layer, and a
hole-blocking layer. More advantageously, the compound is
incorporated as a host material in the light-emitting layer
comprising a phosphorescent dopant.
The materials for phosphorescent dopants to be used in the
light-emitting layer are preferably organic metal complexes
containing at least one metal selected from ruthenium, rhodium,
palladium, silver, rhenium, osmium, iridium, platinum, and gold.
Such organic metal complexes are well known in the aforementioned
patent documents and elsewhere and a suitable complex can be
selected from them and used in this invention.
Preferable phosphorescent dopants include complexes containing a
noble metal element such as Ir in the center, typically Ir(ppy)3,
complexes such as Ir(bt)2.acac3, and complexes such as PtOEt3.
Examples of these complexes are shown below, but are not limited
thereto.
##STR00016## ##STR00017## ##STR00018## ##STR00019##
The content of the aforementioned phosphorescent dopant in the
light-emitting layer is in the range of 2-20 wt %, preferably in
the range of 5-10 wt %. In this case, the compound for organic EL
device of this invention is preferably used as a host material and
it is incorporated in the light-emitting layer while controlling
its content at 50 wt % or more, preferably in the range of 80-95 wt
%.
The structure of the organic EL device of this invention will be
explained next with reference to the drawing, but it is not limited
to the one illustrated in the drawing.
FIG. 1 schematically shows an example of the structure of an
organic EL device generally used in this invention and the symbols
in FIG. 1 stand for the following: 1 for a substrate, 2 for an
anode, 3 for a hole-injecting layer, 4 for a hole-transporting
layer, 5 for a light-emitting layer, 6 for an electron-transporting
layer, and 7 for a cathode. The organic EL device of this invention
comprises a substrate, an anode, a light-emitting layer, and a
cathode as essential layers; in addition, the device preferably
contains a hole-injecting/transporting layer and an
electron-injecting/transporting layer and, further, a hole-blocking
layer disposed between the light-emitting layer and the
electron-injecting/transporting layer. The term
hole-injecting/transporting layer means a hole-injecting layer
and/or a hole-transporting layer while the term
electron-injecting/transporting layer means an electron-injecting
layer and/or an electron-transporting layer.
The substrate 1 serves as a support for an organic EL device and
the materials useful therefor include a quartz plate, a glass
plate, a metal sheet, a metal foil, a plastic film, and a plastic
sheet. In particular, a glass plate is preferred.
The anode 2 plays a role of injecting holes into the hole-injecting
layer 3. The anode 2 is usually constituted of a metal such as
aluminum, gold, silver, nickel, palladium, and platinum, a metal
oxide such as an oxide of indium and/or tin (ITO), a metal halide
such as copper iodide, carbon black, or an electrically conductive
polymer such as poly(3-methylthiophene), polypyrrole, and
polyaniline.
The light-emitting layer 5 is constituted of a light-emitting
substance that emits light when excited by recombination of holes
injected from the anode 2 and migrating through the
hole-transporting layer 4 and electrons injected from the cathode 7
and migrating through the electron-transporting layer 6 upon
application of an electrical field to the electrodes. The
light-emitting layer 5 preferably comprises a dopant material and a
host material consisting of the aforementioned compound for organic
EL device as a light-emitting substance.
The cathode 7 plays a role of injecting electrons through the
electron-transporting layer 6 into the light-emitting layer 5. The
materials useful for the cathode 7 are preferably metals of low
work function for efficient injection of electrons and examples
include metals such as tin, magnesium, indium, calcium, cesium,
aluminum, and silver and alloys thereof. Examples of the alloys
include magnesium-silver alloys, magnesium-indium alloys, and
aluminum-lithium alloys.
The hole-injecting layer 3, the hole-transporting layer 4, and the
electron-transporting layer 6 are optional organic layers; the
hole-injecting layer 3 is used for the purpose of enhancing the
efficiency of injecting holes from the anode 2 into the
hole-transporting layer 4 while the hole-transporting layer 4 and
the electron-transporting layer 6 respectively transport holes and
electrons to the light-emitting layer 5. An electron-injecting
layer may be disposed between the cathode 7 and the
electron-transporting layer 6. The materials useful for these
layers are well known.
The materials for the hole-injecting layer include phthalocyanine
compounds such as copper phthalocyanine (CuPC), organic compounds
such as polyaniline and polythiophene, and oxides of metals such as
vanadium, ruthenium, and molybdenum.
The materials for the hole-transporting layer include triazole
derivatives, oxadiazole derivatives, imidazole derivatives,
polyarylalkane derivatives, pyrazoline derivatives, pyrazolone
derivatives, phenylenediamine derivatives, arylamine derivatives
such as NPB, amino-substituted chalcone derivatives, oxazole
derivatives, styrylanthracene derivatives, fluorenone derivatives,
hydrazone derivatives, stilbene derivatives, silazan derivatives,
aniline-based copolymers, and electrically conductive oligomers,
especially thiophene oligomers.
The materials for the electron-transporting layer include metal
complexes such as Alq3, 10-hydroxybenzo[h]quinoline metal
complexes, oxadiazole derivatives, distyrylbiphenyl derivatives,
silole derivatives, 3- or 5-hydroxyflavone metal complexes,
benzoxazole metal complexes, benzothiazole metal complexes,
trisbenzimidazolybenzene, quinoxaline compounds, phenanthroline
derivatives, 2-t-butyl-9,10-N,N'-dicyanoanthraquinonediimine,
n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide,
and n-type zinc selenide.
It is possible to build a structure that is the reverse of the
structure shown in FIG. 1 by piling the cathode 7, the
electron-transporting layer 6, the light-emitting layer 5, the
hole-transporting layer 4, and the anode 2 one upon another in this
order on the substrate 1. As described earlier, it is also possible
to dispose the organic EL device of this invention between two
substrates at least one of which is highly transparent. In this
case of the reverse structure, it is also possible to add or omit a
layer or layers as needed.
The organic EL device of this invention is applicable to a single
device, a device with its structure arranged in array, or a device
in which the anode and the cathode are arranged in X-Y matrix. This
invention provides an organic EL device that is enhanced in the
luminous efficiency and markedly improved in the driving stability
compared with the conventional devices utilizing emission of light
from the excited singlet state by incorporating a compound of a
specified skeleton and a phosphorescent dopant in the
light-emitting layer and the device can perform excellently in
applications to full-color or multicolor panels.
EXAMPLES
This invention will be explained in more detail below with
reference to the examples; however, this invention is not be
limited to these examples and it can be reduced into practice in a
variety of modes unless such a mode of practice exceeds the
substance of this invention. The compound numbers in the examples
correspond to the numbers assigned to the chemical formulas earlier
cited in the specification.
Example 1
##STR00020##
In a nitrogen-blanketed 2,000-ml three-necked flask were placed
33.3 g (297.0 millimoles) of 1,2-cyclohexanedione and 86.0 g (594.7
millimoles) of phenylhydrazine hydrochloride, then 1,000 ml of
ethanol was added, and the mixture was stirred. Thereafter, 3.0 g
(30.6 millimoles) of concentrated sulfuric acid was added dropwise
to the flask over 5 minutes and the resulting mixture was heated to
65.degree. C. and stirred for 4 hours. The mixture was then cooled
to room temperature, the purplish brown crystals formed were
collected by filtration, and the crystals were reslurried twice in
500 ml of ethanol and then dried under reduced pressure to yield
80.0 g (280.5 millimoles, 96.3% yield) of a purplish brown
powder.
Then, 72.0 g (261.5 millimoles) of the aforementioned purplish
brown powder was placed in a 1,000-ml three-necked flask, then 720
g of acetic acid and 72.0 g of trifluoroacetic acid were added, and
the mixture was stirred. The mixture was then heated to 100.degree.
C. and stirred for 15 hours. The mixture was cooled to room
temperature, the yellow crystals formed were collected by
filtration, and the crystals were rinsed with 200 ml of acetic
acid, then rinsed with 200 ml of hexane, and dried under reduced
pressure to yield 30.0 g (117.1 millimoles, 44.8% yield) of white
powder A'. White powder A' thus obtained is
indolo[2,3-a]carbazole.
##STR00021##
Next, 26.0 g (101.4 millimoles) of the white powder obtained above,
122.7 g (601.4 millimoles) of iodobenzene, 54.7 g (287.2
millimoles) of copper iodide, 66.7 g (482.6 millimoles) of
potassium carbonate, and 800 ml of quinoline were placed in a
nitrogen-blanketed 1,000-ml three-necked flask and the mixture was
stirred. Then, the mixture was heated to 190.degree. C. and stirred
for 72 hours. The mixture was cooled to room temperature, 500 ml of
water and 500 ml of dichloromethane were added, the mixture was
stirred, and the yellow crystals formed were collected by
filtration. The filtrate was transferred to a 2,000-ml separatory
funnel and separated into an organic layer and an aqueous layer.
The organic layer was washed three times with 500 ml of water,
dehydrated over magnesium sulfate, the magnesium sulfate was
filtered off, and the solvent was distilled off under reduced
pressure. The residue was purified by column chromatography to
yield 13.7 g (41.2 millimoles, 40.6% yield) of white solid A. White
solid A thus obtained is 11-phenylindolo[2,3-a]carbazole.
##STR00022##
In a nitrogen-blanketed 100 ml three-necked flask were placed 0.52
g (2.33 millimoles) of palladium(II) acetate, 1.97 g (9.74
millimoles) of tri-tert-butylphosphine, and 45 ml of dehydrated
xylene and the mixture was stirred. The mixture was then heated to
80.degree. C. and stirred for 30 minutes to prepare the catalyst.
Next, 15.4 g (46.3 millimoles) of 11-phenylindolo[2,3-a]carbazole,
14.5 g (69.7 millimoles) of 3-bromoquinoline, 18.8 g (195
millimoles) of sodium tert-butoxide, and 430 ml of dehydrated
xylene were placed in a nitrogen-blanketed 1,000-ml three-necked
flask and the mixture was stirred. The mixture was heated to
80.degree. C., the catalyst solution prepared above was added, and
the resulting mixture was heated to 130.degree. C. and stirred for
17 hours. The mixture was cooled to room temperature, 340 ml of
water added and stirred, and the yellow crystals formed were
collected by filtration. The crystals were reslurried twice in 200
ml of methanol, purified by column chromatography, and then
reslurried in toluene by application of heat to yield 12.0 g (26.1
millimoles, 56.4% yield) of yellow crystals. This yellow
crystalline product is Compound 3. APCI-MS, m/z 460
[M+H].sup.+.
Example 2
An organic EL device constituted as in FIG. 1 with addition of an
electron-injecting layer was fabricated. Applying the vacuum
deposition process at a degree of vacuum of 4.0.times.10.sup.-4 Pa,
the constituent layers were deposited in thin film one upon another
on a glass substrate on which a 150 nm-thick ITO anode had been
formed. First, copper phthalocyanine (CuPC) was deposited on the
ITO anode to a thickness of 20 nm as a hole-injecting layer. Then,
NPB was deposited to a thickness of 40 nm as a hole-transporting
layer. Next, Compound 3 as a host material and Ir(ppy)3 as a dopant
were co-deposited from different evaporation sources on the
hole-transporting layer to a thickness of 35 nm to form a
light-emitting layer. At this point, the concentration of Ir(ppy)3
was 7.0 wt %. After this, Alq3 was deposited to a thickness of 40
nm as an electron-transporting layer. Further, lithium fluoride
(LiF) was deposited on the electron-transporting layer to a
thickness of 0.5 nm as an electron-injecting layer. Finally,
aluminum (Al) as an electrode was deposited on the
electron-injecting layer to a thickness of 170 nm to complete the
fabrication of the organic EL device.
The organic EL device thus fabricated was connected to an outside
power source and, when direct current voltage was applied, the
device was confirmed to emit light with the characteristics shown
in Table 1. In Table 1, the luminance, voltage, and luminous
efficiency were measured at 10 mA/cm.sup.2. The maximum wavelength
of the spectrum of light emitted from the device was 517 nm and
this proves that light is emitted from Ir(ppy)3.
Example 3
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 2 as a host material in the
light-emitting layer.
Example 4
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 9 as a host material in the
light-emitting layer.
Example 5
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 18 as a host material in the
light-emitting layer.
Example 6
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 20 as a host material in the
light-emitting layer.
Example 7
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 23 as a host material in the
light-emitting layer.
Example 8
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 26 as a host material in the
light-emitting layer.
Example 9
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 29 as a host material in the
light-emitting layer.
Example 10
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 31 as a host material in the
light-emitting layer.
Example 11
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 33 as a host material in the
light-emitting layer.
Example 12
An organic EL device was fabricated as in Example 2 with the
exception of using Compound 35 as a host material in the
light-emitting layer.
Comparative Example 1
An organic EL device was fabricated as in Example 2 with the
exception of using HMTPD in the hole-transporting layer and TAZ as
a host material in the light-emitting layer.
Comparative Example 2
An organic EL device was fabricated as in Example 2 with the
exception of using TAZ as a host material in the light-emitting
layer.
The luminous characteristics were evaluated and the results are
shown in Table 1. In Table 1, the luminance, voltage, and luminous
efficiency were measured at 10 mA/cm.sup.2. In each of Examples 2
to 12 and Comparative Examples 1 and 2, the maximum wavelength of
the spectrum of light emitted from the device was 517 nm and this
proves that light is emitted from Ir(ppy)3.
TABLE-US-00001 TABLE 1 Luminous Compound Luminance Voltage
efficiency No (cd/m.sup.2) (V) (1 m/W) Example 2 3 2620 5.2 15.8 3
2 2760 6.2 14.0 4 9 3150 6.5 15.2 5 18 2850 6.9 13.0 6 20 2945 5.1
18.1 7 23 2860 5.2 17.3 8 26 2560 5.5 14.6 9 29 3020 5.2 18.2 10 31
2975 5.4 17.3 11 33 3040 5.6 17.1 12 35 2080 6.7 9.8 Comparative --
2050 13.2 4.9 example 1 2 -- 1270 9.5 4.2
INDUSTRIAL APPLICABILITY
The organic EL device of this invention is capable of emitting
light of high luminance at high efficiency with application of low
voltage. Hence, the device is of high technical value because of
its potential applicability to flat panel displays (for example, in
office computers and wall-hanging television sets), vehicle-mounted
display devices, mobile phone displays, light sources utilizing the
characteristics of planar light emitters (for example, light
sources for copiers and backlight sources of liquid crystal
displays and instruments), signboards, and beacon lights.
* * * * *